A typhoon is a tropical storm in the Pacific Ocean with extremely high wind speeds. The graphs below show the number of recorded typhoons in the Eastern Pacific and the Western Pacific each year between the years of 1997 and 2010.
A simple moving average is defined as the average of data values for several consecutive increments. For instance, the four-year moving average of the typhoon frequencies for the year 2008 is the average of the number of typhoons in the years 2005, 2006, 2007 and 2008.
region of the Pacific has greater year-to-year variability in typhoon frequency.
The proportion of years recorded in the Western Pacific with more than 30 typhoons is
the proportion of years recorded in the Eastern Pacific with less than 20 typhoons.
For the Western Pacific region, the difference between the highest and lowest four-year simple moving averages that are possible to calculate given the data shown in the graphs is